Grinding spur and helical gears with a threaded grinding wheel is well known in gear manufacture. Equally well known is the need to periodically dress the grinding wheel, usually with a diamond tool, to remove dull abrasive grains, clear the chip-loaded surface of the grinding wheel, or, shape the grinding wheel to a specific profile in order to generate a desired work gear tooth profile.
One example of dressing a threaded grinding wheel to provide a specific grinding profile is shown in U.S. Pat. No. 2,792,824 to Rickenmann. The disclosed method utilizes a pair of diamond dressing tools which are traversed in multiple passes across the width of a threaded grinding wheel in a direction parallel to the wheel axis. Prior to each traversal, the tools are stepwise adjusted along the grinding wheel flanks to reposition the tool for the next dressing pass.
In dressing a grinding wheel for grinding involute gear tooth profiles according to U.S. Pat. No. 2,792,824, a straight line flank profile is most commonly dressed into the grinding thread of the wheel to produce an involute tooth profile on the work gear. However, in those instances where a non-involute gear profile is to be ground, modifications to the grinding wheel straight line flank are included in the dressing process. Templates are used to cause the diamond tools to deviate from the straight-line flank dressing on the grinding wheel. The modified thread or rib is dressed completely along the wheel width. Therefore, the same flank profile form appears along the entire length of the grinding thread thus forming the same profile shape along the entire length of the tooth being ground.
Dressing a threaded grinding wheel along its line of action is disclosed by U.S. Pat. No. 2,907,314 to Osplack. The dressing tool traverses in multiple passes along the line of action of the rack form of a rotating grinding wheel. The tool is incrementally adjusted in a direction perpendicular to the line of action prior to each pass so as to reposition the tool for the following traversal.
There are situations where it is desirable to manufacture a gear having a modified tooth form which deviates from a true involute, such as when deflection must be taken into account due to heavy operating loads. One or both flanks of a tooth may be modified depending on the direction of rotation of the gear. Osplack teaches modifying the flanks of the grinding wheel to effect changes in the tooth flanks of a work gear wherein a roller and cam surface are used to control the amount a dressing tool deviates from a straight-line grinding profile.
As with the previous teaching in U.S. Pat. No. 2,792,824, modifications introduced into the grinding thread profile by the method of U.S. Pat. No. 2,907,314 extend along the entire length of the grinding thread. Therefore, any subsequent modification formed in the tooth profile will be formed along the entire length of the tooth.
U.S. Pat. No. 3,568,655 to Deakin et al. discloses yet another manner wherein flank variation is introduced in a threaded grinding wheel. As slides are moved to reposition the dressing tools for a dressing pass, a plate (mounted on one or both of the slides) having a cam surface engages a lever to control small lateral movements of the dressing tool in the direction of the grinding wheel axis. The small movements represent deviations from a straight-line grinding profile and produce variations from a true involute along the entire length of the tooth flanks of a work gear.
However, all of the dressing methods discussed above introduce a uniform profile change along the entire length of the grinding thread and hence, create a uniformly modified tooth profile along the entire length of a gear tooth. It has not been possible to differentially modify a tooth profile along the tooth length even though conditions, such as load and wear, are not constant along the gear tooth length.
It is an object of the present invention to afford better control of the surface topography of a gear tooth by controlling the profile shape at different locations along the length of the gear tooth.
It is another object of the present invention to provide a novel method of dressing a threaded grinding wheel whereby multiple tooth profile regions may be formed along the tooth length of a gear to be ground by the dressed grinding wheel.